This is a bit unexpected, but when specifying a require in a test's tmt, this then applies it to the whole plan that calls it. It is more natural to assume that the require is only added to the specific test:

Example: https://github.com/scikit-build/scikit-build-core
The /examples plan runs all tests in /docs/example where for example in /docs/example/getting_strated/fortran it has:

require+:
  - gcc-gfortran

It is preferred that these dependencies do not porpagate to the other tests in order to keep the testing environments clean from each other.